Theoretical investigation of experimentally determined α-effects - The role of electronics

Recent experimental reports involving both alpha-nucleophiles and normal nucleophiles have reported both the presence and absence of an alpha-effect. In ester systems, such as dimethylmethylphosphonate (DMMP), a small alpha-effect is reported, but the reference point is a stationary point of the potential energy surface that must rearrange to acquire the near attack conformation (NAC) necessary for the Sn2 pathway to proceed. The second type of study involves use of highly fluorinated alkoxides as normal nucleophiles and reports no alpha-effect. This paper employs linear free energy plots in an investigation of electronic effects in methyl formate S(N)2 reactions, using high-level computations of transition states for determination of energy barriers.